1. Field of the Invention
The present invention relates to the electrodeposition of single crystal tin, doped tin and other single crystals by electrolysis from electrolytic baths containing tin or other cations. The invention also relates to the use of the resulting material, for example, as infrared detectors or as an epitaxial substrate which can be used to provide good single crystalline tin material for epitaxial growth of certain semiconductors, and to the use of the resulting systems as, for example, photovoltaic cells or infrared detectors. Electrodeposition of semiconductor materials such as CdTe or HgTe on the tin material is also taught.
2. Description of the Prior Art
The electrodeposition of polycrystalline tin and doped tin is now broadly known in the art. Many standard tin plating baths, both acid and alkaline, with or without various additives have been employed to achieve results such as brightening, leveling, adhesion to the cathode, superconductivity, as well as other objectives. When such additives are used they often tend to insure that the tin deposits are polycrystalline, and thus flat or bright, rather than single crystal. However, in substantially each and every one of these prior art tin electrodeposition processes, the tin has been deposited directly onto a cathodic substrate. This has also consistently resulted in the production of tin that is polycrystalline, and that includes, in both an "electrical" and "crystallographic" sense, voids, misalignments, and discontinuities which render the tin inefficient for use as an oriented epitaxial substrate or as an electrical contact.
Tin has been one of several conductive metals which has been found to be useful as a nucleating surface possessing favorable electrical characteristics for use with semiconductive materials. However, the use of most prior art tin with semiconductor materials has not provided either single crystal epitaxy or good electrical contact, thus reducing device efficiency. This inefficiency has been due to discontinuous surface morphology, voids, and misalignments that polycrystalline tin provides to semiconductor materials.
Electrodeposition of various semiconductor materials, such as HgTe or CdTe, has been attempted and reported in the past. However, due to the substantial differences among the reduction potentials of Hg, Cd, and Te, the ability to deposit stoichiometric HgTe, CdTe, or ternary mixture compounds from prior systems is suspect. The ability to electrodeposit stoichiometric HgTe on single crystal cubic tin has not been previously reported. The same problems have been noted as to compounds of Group III and Group V materials.
Accordingly, it is an object of this invention to provide processes for the electrodeposition of single crystal tin that is substantially free of voids, misalignments, and discontinuities.
A further object is to provide tin materials that are capable of more functional epitaxial contact with semiconductor materials.
More specifically, it is an object to provide a process in which single crystal tin so produced can be combined with various semiconductor materials to form a photovoltaic cell or any other device which would benefit from the favorable single crystalline characteristics.
Still another object is to provide processes for the electrodeposition of semiconductor materials, such as compounds of Group III and Group V, HgTe, and CdTe, in true stoichiometric proportions, with appropriate doping.
Another object is to provide the use of doped single crystal tin in an infrared detector system.
Other objects, features, and advantages of this invention will be apparent from the following description, drawings, and examples.